The concept of embedding optical fibers in molded articles is not new. For example, U.S. Pat. No. 3,910,105 "Method for Detection of Flaws and Composite Fiberglass Structures" by D. J. Hoffstedt discloses a method for embedding optical fibers within molded structures. However, Hoffstedt generally limits his discussion to the incorporation of the optical fiber on a bond line between a face sheet and honeycomb core. Although the optical fiber is relatively small in diameter it creates a local discontinuity between the face sheet and honeycomb core. In molded composites, composed of filamentary reinforcement sheets preimpregnated with a resin, the sheets are individually layed up in a mold to form a preform which is subsequently molded. If the resin is a thermosetting type it is typically heated past the point of melting and flows to form a homogenous matrix and thereafter cures. If the resin is a thermoplastic it is also heated to a point wherein it melts but no chemical change occurs. The Hoffstedt approach could also be applied to these types of composite structures. However, if the optical fiber is embedded into such a composite structure composed of filamentary material (fibers) in a resin matrix, problems occur; the primary being that when an optical fiber is embedded, such that it is not parallel to adjacent fibers, these fibers must bend around the much larger diameter optical fiber, creating a structural weak point. In the past, with the Hoffstedt method this phenomenon could not be overcome except by always employing the optical fibers in parallel arrangement to adjacent structural fibers.
Applicants copending application, Ser. No. 735,619 "Method of Testing Composite Structures", filed May 20, 1985, discloses a significant improvement to the process of incorporate optical fibers in both of these types of structures by first arranging on or embedding the optical fiber in a layer of resin and thereafter laying it up into the mold. Thus, structural fibers which are not parallel to the optical fiber are not subjected to the radical bending to get around the optical fiber, but curve gradually therearound. Thus, this later invention provides the ability to arrange the optical fiber in efficient patterns instead of, as in the past, always placing the optical fiber parallel to the structural fibers. However, neither of these methods addressed the problem of how to effectively couple the embedded optical fiber to external optical fibers. In the past the optical fibers were just extended out of the molded structure which caused several problems:
(1) The mold had to somehow accommodate the free end of the optical fiber extending out of the layed up structure.
(2) The molding process and/or subsequent handling and installation of the structure into other assemblies would cause breakage of the optical fiber, particularly at the point of exiting from the structure.
(3) Most molded structures are trimmed after molding which requires that the optical fiber be cut at this point greatly complicating the coupling of an external optical fiber thereto. It is readily apparent that this is not a desirable thing to do.
There are numerous methods in the prior art for coupling optical fibers to each other. For example, U.S. Pat. No. 4,183,737 "Method of Joining Optical Fibers with a Link Piece" by M. Chown et al., U.S. Pat. No. 4,477,146 "Optical Waveguide Connector" by T. P. Bower et al., U.S. Pat. No. 4,487,474, "Optical Connector with Ceramic Plugs and Sleeve" by M. Nishie et al., U.S. Pat. No. 4,519,672 "Method for Obtaining an Accurate Concentric Fastening of an Optical Fibre in a Connector" by I. Rogstadius, U.S. Pat. No. 4,529,265, "Optical Fiber Joints and Method of Joining Optical Fibers" by S. Toya et al., U.S. Pat. No. 4,537,468 "Reinforced Optical Fiber Butt Weld Connection" by B. Degoix et al., U.S. Pat. No. 4,454,234, "Low Loss Optical Fiber Splicing" by G. F. DeVeau Jr. et al., and U.S. Pat. No. 4,580,874, "Optical Fiber Cable Repair and Joining Technique and Kit for Performing the Same" by J. Winter et al., U.S. Pat. No. 4,478,485 "Connector for Coupling at Least One Optical Fiber to a Further Optical Element" by Khoe et al. All these coupling devices require access to the ends of both of the optical fibers to be joined and are not applicable to the problem at hand.
Thus, it is a primary object of the subject invention to provide a method of connecting optical fibers within a molded structure to external optical fibers.
It is another primary object of the subject invention to provide a method of embedding optical fibers within a molded structure, requiring peripheral trimming to a final shape after molding, to an external optical fiber.
It is a further object of the subject invention to provide a method of embedding optical fibers within a molded structure while providing a simple means of joining the embedded optical fiber to an external optical fiber.
It is a still further object of the subject invention to provide a method of embedding optical fibers within a molded structure, wherein the connection between the embedded optical fiber and the external optical fiber require little or no space and does not unduly effect the strength of the structure nor complicates the design thereof.